[Heathkit] AG-9A/IG-72????

[Mike McCarty]

Alexander N Gerli Sr wrote:
> Hello, Friends!
> 
> Sorta-stupid question.: is the IG-72 Audio Generator really a AG-9A in a
> newer package?

Not quite. There are a couple of changes between them. The circuit
is essentially the same, but some resistors in the IG-72 have higher
ratings than in the AG-9A. The 47K plate load resistor for the 6AU6
is changed from 1W in the AG-9A to 2W in the IG-72. It's hard for
me to read but it looks like the screen load resistor for that
tube was also changed from 150K to 120K. There are some slight
differences between the "dial setting" and the value of R1 and
R2. I see these differences

dial setting 70, R1 (IG-72) = 14.9K vs R1 (AG-9A) = 14.3K
dial setting 5, R2 (IG-72) = 190K vs R2 (AG-9A) = 194K
dial settin 10, R2 (IG-72) = (not given in table) vs
	R2 (AG-9A) = 98(?)K the "8" might be different, hard for me
to read

Otherwise, the circuits appear identical, AFAICT.

Mike
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